Plant Responses Flashcards
Why do plants respond to their environment?
To increase their chances of survival, they respond to their environmental changes (e.g. light and gravity) this is called tropisms
Describe and explain what abiotic stress is
Abiotic stress is anything thats potentially harmful to a plant thats natural, but non-living, like a drought (water stress).
Plants can respond to abiotic stress, e.g. some respond to extreme cold by producing their own form of antifreeze
E.g. carrots produce antifreeze proteins at low temps - the proteins bind to ice crystal and lower the temperature that water freezes, stopping more ice crystals from growing
Describe and explain herbivory
Herbivory is when plants are eaten by animals (including insects).
Plants have chemical defences that they use against herbivory e.g. they can produce toxic chemicals in response to being eaten
E.g.
- Alkaloids - these are chemicals with bitter tastes, noxious smells or poisonous characterises that deter or kill herbivores e.g. tobacco plants produce the alkaloid nicotine in response to tissue damage. Nicotine is highly poisonous to many insects
- tannins - these taste biter and in some herbivores (e.g. cattle, sheep) they can bind to proteins in the gut, making the plant hard to digest. This deters animals from eating the pant
- some plants release pheromones in response to herbivory.
Pheromones are signalling chemicals that produce a response in other organisms
E.g some plants release pheromones into the air in response to herbivore grazing. This can cause nearby plants that detect these chemicals to start making chemical defences such as tannins
Other plants are able to fold up in response to being touched (this can scare off animals that to eat it or knock of small insects that feed on the plant
Define tropism
The response of a plant to a directional stimulus.
Positive tropism is growth towards the stimulus
Negative tropism is growth away from the stimulus
Describe and explain phototropism
- the growth of plant in response to light
- shoots are positively phototropic (grow towards light)
- roots are negatively phototropic (grow away from light)
Describe and explain geotropsim/ gravitropism
- the growth of a plant in response to gravity
- shoots are negatively geotropic and grow upwards
- roots are positively geotropic and grow downwards
State and describe other tropisms
- hydrotropism - plant growth in response to water. Roots are positively hydrotropic
- thermotropism - plant growth in response to temperature
- thigmotropism - plant growth in response to contact/ touch with an object
Describe and explain plant growth hormones
Plants respond to some stimuli using growth hormones - these are chemicals that speed up or slow down plant growth.
- growth hormones are produced in shoot tips and root tips (growing regions) and they move to where they’re needed in other parts of the plant
Describe and explain role gibberellin
- it is a growth hormone that stimulates seed germination, stem elongation, side shoot formation and flowering
Describe and explain role of auxins
- stimulate the growth of shoots by cell elongation
- produced in the tips of shoots in flowering plants and diffuse backwards to stimulate the cells
- if the tip of a shoot is removed, no auxin will be available and the shoot stops growing. Auxins stimulate growth in shoots but high concentrations inhibit growth in roots
Describe and explain what indoleacetic acid (IAA) is
- a type of auxin that is produces in the tips of shoots and roots in flowering plants
- its moves by diffusion and active transport over short distances and via the phloem over long distances
- this results in different parts of the plant having different amount of IAA
The uneven distribution of IAA means there’s uneven growth of the plant
(Root growth is inhibited by high conc of IAA, but high concentration of IAA promotes shoot growth)
